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N007-M2 Tier 1 · Foundations · medium ecommerce · Brightlane

Return each product's name and stock value, sorted from highest stock value to lowest

Part of ORDER BY and Result Sorting in SQL

The problem

Brightlane's inventory team is prioritising restock decisions and wants to see the highest-value stock positions first. Stock value for a product is its unit price multiplied by stock_qty (the number of units currently in stock).

Write a query to return each product's name and stock value, sorted from highest stock value to lowest.

Assumptions:

  • The products table contains every product in Brightlane's catalogue.
  • When two products share the same stock value, the one whose name comes first alphabetically should appear first.
  • The computed stock-value column should be aliased as stock_value in the output, and that alias can be referenced directly in the ORDER BY clause.

Output:

  • One row per product, with columns name and stock_value, sorted by stock_value descending, then by name ascending.
Schema · ecommerce 5 tables
categories
id integer
name text
parent_id? integer
products
id integer
name text
category_id integer
price numeric
stock_qty integer
attributes? jsonb
order_items
id integer
order_id integer
product_id integer
quantity integer
unit_price numeric
customers
id integer
name text
email text
city? text
country text
created_at timestamptz
is_active boolean
orders
id integer
customer_id integer
ordered_at timestamptz
status text
total_amount numeric
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Solution query
SELECT
  name,
  price * stock_qty AS stock_value
FROM
  products
ORDER BY
  stock_value DESC,
  name

The shape

The alias stock_value is defined in the SELECT and reused directly in the ORDER BY — one expression, written once, used twice.

Clause by clause

  • SELECT name, price * stock_qty AS stock_value computes the per-product stock value inline and gives it a name. The multiplication runs once per row, against that row's price and stock_qty, and the alias labels the resulting column so it reads as a domain quantity rather than as the raw arithmetic.
  • FROM products reads the catalogue.
  • ORDER BY stock_value DESC, name sorts by the computed value descending so the highest-value stock positions land first, then alphabetises any rows whose stock_value ties. The second sort key picks the name column directly — no DESC, so it defaults to ascending.

Why this and not retyping price * stock_qty

The alternative — ORDER BY price * stock_qty DESC, name — returns the same rows in the same order. PostgreSQL evaluates the expression a second time, but the cost is invisible to the user. The reason to prefer the alias is readability: writing the expression once means there's only one place to edit if the stock-value formula ever changes, and no risk of the two copies drifting apart.

ORDER BY is one of the few clauses where a SELECT-list alias is available, and the reason is evaluation order. SELECT runs before ORDER BY, so by the time the sort happens, the alias already names a real output column. Try the same trick in WHERE, which runs before SELECT, and PostgreSQL raises an error because the alias doesn't exist yet.

You practiced sorting on a SELECT-list alias. ORDER BY runs after SELECT, so any alias defined there is available as a sort key — the recurring shape any time you want to sort by a derived value without retyping its expression.

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